One embodiment of the present invention generally relates to a connector or cable connector assembly, and more particularly, to a connector or cable connector assembly with an equalization circuit board for performing signal conditioning.
Conventional cable assemblies have been proposed that include an electrical cable with multiple electrical contacts and a housing attached to the cable. Signal conditioning circuit elements have been provided, such as resistors, capacitors and inductors, that are mounted in the housing as discrete individual components connected to contacts within the housing. U.S. Pat. No. 5,766,027 describes a cable assembly with an equalization board, on which the discrete signal conditioning circuitry is mounted. The circuitry on the equalization board is aligned with and joined to electrical contacts and cable conductors.
FIG. 1 illustrates a conventional equalization circuit board 10 having conductive pads 12 along one edge and a separate array of conducting pads along the opposite edge of the opposite side. The circuit board 10 may include multiple layers, such as upper, central and bottom layers. The central layer may include a conducting ground plane referenced to electrical ground with plating lined apertures (vias) 14. The plating lined vias 14 extend between the upper layer and bottom layer. The plating within the vias 14 establishes electrical connections on the upper and lower layers to the ground plane. Signal conditioning circuitry is included on the upper or lower layer in the form of multiple conducting pads 16 and multiple relatively narrow circuit paths 18 interconnecting various conducting pads 16 and various plating lined vias 14. Each conducting pad 16 is identified with an impedance symbol, such as R or L or C to indicate electrical elements that provide signal conditioning.
High speed data signals are conveyed at a desired data rate from a cable through the cable connector assembly. The data rate includes a known fundamental frequency. The data signals are comprised of multiple frequency components, each frequency component of which is attenuated to a differing degree by the cable.
FIG. 2 illustrates an exemplary graph of an attenuation characteristic curve 24 over an operating frequency range exhibited by high speed data signals. The curve 24 of FIG. 2 may also be considered a cable loss curve. The horizontal axis of the graph in FIG. 2 represents frequency, while the vertical axis represents xe2x80x9cdecreasingxe2x80x9d attenuation. Attenuation increases in the direction of arrow 20. Thus, low frequency components of data signals experience less attenuation due to cable loss than high frequency components of the data signals. The curve 24 corresponds to a data signal that is transmitted at a known desirable data rate having a fundamental frequency fFND. The data rate similarly has a frequency component at a second harmonic f2nd. Heretofore, it was considered desirable to maintain the level of attenuation for all frequency components of a data signal within a close tolerance (i.e., substantially constant). Heretofore, it was believed that the variations in attenuation introduced undesirable signal characteristics into the data stream.
In the past, signal conditioning circuits, such as disclosed in the ""027 patent, were proposed for adjusting the cable loss characteristic to maintain substantially constant attenuation over the entire operating frequency range of the connector assembly. FIG. 2 illustrates (through a dashed line) a signal conditioning equalization attenuation curve 22, that is attained by conventional signal conditioning circuits. The signal conditioning circuit creates an attenuation curve that mirrors, but is inverted with respect to, the cable loss curve 24 to add exponentially decreasing attenuation to the data signal over frequency. The combined effects of the signal conditioning circuit and cable form equalization curve 22. The equalization curve 22 represents the attenuation characteristic of the data signal output from the connector assembly once the data signals have traveled through the signal conditioning circuitry on equalization board 10 (FIG. 1). As illustrated in FIG. 2, conventional signal conditioning circuitry is designed to offset the portion of the cable loss curve 24 below the second harmonic f2nd, such that frequency components of the data signal below the second harmonic f2nd, or fundamental frequency fFND exhibit constant attenuation. Thus, conventional signal conditioning circuitry introduced additional attenuation corresponding to region 26 above the equalization curve 22 and below the cable loss curve 24 up to the second harmonic f2nd, or fundamental frequency fFND.
Conventional signal conditioning circuits used multiple signal conditioning components including several capacitors, several resistors and several inductors to attain the desired equalization curve 22. In many systems, ten or more components were required. The components were then organized on an equalization board in a layout dictated by the efficient use of the surface area of the equalization board. The components were distributed and arranged across the surface of the equalization board in a layout needed to maximize the useable area on the board, in order to minimize the size of the board. The most space efficient layouts for the multiple circuit components required that the components be interconnected through curved traces running in multiple directions and including multiple bends. Conventional signal conditioning circuit layouts have failed to realize that the shear complexity of the circuit layout introduces additional sources of interference into the data signals being transmitted. For instance, conventional signal conditioning circuit layouts introduce reflectance, cross-talk and other interference sources that adversely affect the signal integrity. Heretofore, these additional factors affecting signal integrity were not recognized nor accounted for in connection with the design of equalization circuitry.
Moreover, conventional equalization circuits for cable assemblies offer poor signal integrity at high frequencies and are therefore lossy in nature. These equalizing circuits not only introduce attenuation at low frequencies, they also introduce attenuation at high frequencies. In order for existing equalization circuits to be affective, they are only useful with long length cable assemblies (e.g., greater than 20 meters at 1.0 GBPS data rates). By limiting equalization circuits to use with long length cable assemblies, the added attenuation introduced by the equalization circuit at high frequencies is small relative to the amount of attenuation introduced by the length of the cable at high frequencies. Thus, while existing equalization circuits introduce undesired attenuation at high frequencies, the amount of attenuation relative to attenuation introduced by the cable itself is minimal. However, such equalization circuits were not useful with shorter length cables nor with cable assemblies having low attenuation at high frequencies relative to the attenuation of the equalization circuit at the same high frequencies.
A need remains for an improved equalization circuit design. It is an object of at least one embodiment of the present invention to meet the foregoing needs and other objectives that will become apparent from the detailed description, drawings and claims presented hereafter.
In accordance with at least one embodiment of the present invention, an equalizer design has been developed that improves the signal integrity of long length and short length cable assemblies. Improvements in the signal integrity are detectable through examination and measurement of eye pattern openings, jitter and other signal xe2x80x9cgoodness qualitiesxe2x80x9d. The equalizer design in accordance with at least one embodiment of the present invention affords the ability to easily modify a cable assembly to account for changes in cable assembly length, changes in conductor size, changes in data rates and the like. The cable assemblies provided in accordance with at least one embodiment of the present invention are usable with longer cable lengths and faster data rates than heretofore known.
In accordance with an alternative embodiment of the present invention, a cable connector assembly is provided for a cable carrying high speed data signals at a desired data rate and having a known fundamental frequency. The data signals include multiple attenuated frequency components defining an attenuation characteristic curve over an operating frequency range of the data signals. The connector assembly includes a plug adapted to be mounted to a cable and a receptacle connectable to the plug. The connector assembly further includes an equalization circuit board conveying data signals over data paths between the plug and receptacle. The circuit board attenuates frequency components below and substantially up to the fundamental frequency of the data rate, without introducing equalization attenuation into frequency components above the fundamental frequency.
In accordance with at least one embodiment, the circuit board may attenuate frequency components up to approximately 90% of the fundamental frequency. Alternatively, the circuit board may attenuate frequency components up to approximately one-half of the fundamental frequency, without introducing equalization attenuation into frequency components thereabove.
In accordance with at least one alternative embodiment of the present invention, an equalization card is provided for a cable assembly carrying high speed data signals. The cable assembly includes a cable with conductors, a plug housing mounted to the cable and a socket receiving the plug housing. The equalization card includes a circuit board removably received within the plug housing and input and output contacts on the circuit board. The input contacts are connected to conductors of the cable and receive data signals over an operating frequency range. The output contacts are adapted to removably engage the socket. The input and output contacts convey data signals from a cable. Frequency equalizing circuit components are mounted to the circuit board between associated input and output contacts. The circuit components maintain a substantially constant attenuation level for frequency components of the data signal below a predetermined frequency cutoff. The frequency cutoff is less than a second harmonic of a fundamental frequency of the data signal.
In accordance with yet another alternative embodiment of the present invention, a high speed serial data signal embodied in a carrier wave is provided. The data signal carries data at a predetermined data rate having a fundamental frequency. The data signal exhibits a substantially constant attenuation level for frequencies of the data signal below a predefined roll-off frequency. The roll-off frequency is defined to be less than a second harmonic of the fundamental frequency of the data rate.
In alternative embodiments, the roll-off frequency for the high speed data signal may be no greater than the fundamental frequency of the data rate. Alternatively, the roll-off frequency may be no greater than one-half of the fundamental frequency of the data rate. The data signal has a non-monotonically increasing attenuation level for frequencies above the roll-off frequency. The attenuation level for frequencies above the roll-off frequency may be exponentially increasing.